Retrofocus type ultra-wide angle lens

ABSTRACT

A retrofocus type ultra-wide angle lens, having 13 air-spaced elements in four groups, which include, as viewed from the object side of the lens, a first group consisting of two divergent meniscus elements and a convergent meniscus element, a second group consisting of three divergent meniscus elements and a convergent cemented component, a third group consisting of a divergent meniscus element and a positive cemented component, and a fourth group consisting of a convergent element, a divergent element, a convergent meniscus element and a cemented component. A diaphragm is disposed immediately behind the third group.

OR a zgioii u Ill-Cu lJl'dt i Mori [ RETROFOCUS TYPE ULTRA-WIDE ANGLE LENS Ikuo Mori, Kawasaki, Japan [73] Assignee: Nippon Kogaku K.K., Tokyo, Japan [22] Filed: Mar. 21, 1972 [21] Appl. No.: 236,716

[75] Inventor:

[30] Foreign Application Priority Data Mar. 26, 1971 Japan ..46/17297 [52] 0.8. CI. ..350/214, 350/176, 350/177, 350/196 [51] Int. Cl. ..G02b 9/64, G021) 13/04 [58] Field of Search ..350/214, 176, 177, 350/198 [56] References Cited UNITED STATES PATENTS I 3,524,697 8/1970 lsshiki et a]. ..350/198 UX 111 3,728,011 51 Apr. 17, 1973 Primary Examiner-John K. Corbin Attorney-Joseph M. Fitzpatrick et a1.

[57] ABSTRACT,

A retrofocus type ultra-wide angle lens, having 13 airspaced elements in four groups, which include, as viewed from the object side of the lens, a first group consisting of two divergent meniscus elements and a convergent meniscus element, a second group consisting of threedivergent meniscus elements and a convergent cemented component, athird group consisting of a divergent meniscus element and a positive cemented component, and a fourth group consisting of a convergent element, a divergent element, a convergent meniscus element and a cemented component. A diaphragm is disposed immediately behind the third group.

FOURTH I GROUP PATENTEYDRPRITIQB 3.728.011

sum 1 or 2 FIRST FIG. I

SECOND mmo L4L5L6L7GROUP DIAP i ff I. F-

\// FILTER Ll0LuL|2L|3 war PAIEIIIEIIIP I 3728.011

SHEET 2 [IF 2 2 LATERAL SPHERICAL ABERRATION cOMA FoR A HALF ANGLE OF vIEw 59 coMA FoR A HALF ANGLE OF VIEW 55 MARGINAL RAYS M R o (320% OF THE UGHT MEASURED co A FO A HALF ANGLE OF vIEw 50 ON THE lSf TANGENTIAL PLANE) 0.!

2B LATERAL SPHERICAL ABERRATIoN a coMA FoR A HALF ANGLE OF mm 40 COMA FOR A HALF ANGLE OF vIEw 25 L I I LG. I

FIG. 20 FIG. 20 FIG. 2E

SPHERICAL QR B AsT GIvIATIsM DISTORTION CONDITION I 50 /ll I r- F'1 -I o -I o -3% -I% 1 RETRQFOCUS TYPE ULTRA-WIDE ANGLE LENS BACKGROUND OF THE INVENTION view of 1 18 for the total focal lengthf=l 3.2 mm.

2. Description of the Prior Art In a lens of short focal length having a wide angle of view, such as the lens to which the present invention relates, it is very difficult to obtain a predetermined Bi. and even more difficult to obtain the proper quantity of marginal or peripheral light. For example, when the angle of view is 118, the actual quantity of marginal light is only 7 percent due to the cosine biquadratic rule, even when a quantity of light amounting to 100 percent of the lens aperture is introduced, as measured on the first tangential plane. In view of the fact that the value of such marginal light should usually be at least about 20 percent in photographic lenses of the type to which the present invention relates, a very great quantity of light, suchas more-than 300 percent of the lens aperture as measured on the first tangential plane, must be provided. To achieve this, there is an additional requisite, i.e. the coma in the marginal area of the lens must be well corrected. This necessarily requires that the relative aperture of the lens be reduced to a certain degree, with respect to the limitations existing in the correction of the coma in the marginal lens area. On the other hand, when the matter is considered from another viewpoint, i.e. from the viewpoint of aberration, the large angle of view necessarily leads to the creation of large distortions and astigmatism. Taking distortion, for example, a curvature of distortion is already present in a similar wide-angle lens whose angle of view is about 80, and from this fact it is evident that the curvature of distortion will be even greater in lenses having an extremely large angle of view, such as the lens to which the present invention relates. This also holds true for astigmatism, and, therefore, the curvature of astigmatism must be absolutely prevented, in order to introduce a great deal of marginal light, because the coma in the marginal region of the lens tends to be attracted to the meridional plane. Accordingly, the meridional plane must be more undercorrected in the outermost marginal area thari in any other part of the view field. The present invention has been made in view of the problems noted above.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a retrofocus type ultra-wide angle lens system which divergent element, a convergent meniscus element and a composite component. The lens system satisfies th relations:

where R represents the radius of curvature of each element.

The lens system according to the present invention further satisfies the relations: I

where n represents the refractive index of each element and d the inter-vertex distance of each element.

The lens system of the present invention further satisfies the relations:

where d represents the dispersive power of each element.

The lens system further satisfies the relations:

(129 dao dga, Or d21- BRIEF DESCRIPTION OF THE DRAWINGS system according to one embodiment of the present invention; and

FIGS. 2A 2E graphically illustrate various aberrations in the lens system of FIG. 1 for its focal length f 13.2mm.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown a lens system according to the present invention whose arrangement and characteristics will be described hereinafter, except for the filter.

A first group, generally designated by A, consists of three meniscus elements L,, L, and L The elements L, and L, are divergent lenses and the element L is a convergent lens. The respective elements are characterized by the following radii of curvature R.

-3R, R,, 5 (3) where the subscripts attached to R represent the order of the successive lens surfaces as viewed from the object side of the system. Further, in order to avoid an extremely large air space between the marginal areas of elements L and L the radii of curvature R and R of elements L and L, are selected to satisfy the relation:

A second group, generally designated by B, consists of four elements L L L and L The elements L L and L, are meniscus divergent lenses and the element L, is a composite convergent lens. A filter may be interposed between the elements L, and L The elements forming the second group are characterized, as follows:

"1 "a u ia where n and d respectively represent the refractive indices and intervertex distances of the respective elements.

A third group, generally designated by C, consists of two elements L and L,,, L being a meniscus divergent lens and L, being a composite convergent lens. These two elements are characterized as follows: I

7 10 'Y 11 (10 where 'y d represents the dispersive power of each element.

A fourth group, generally designated by D, consists of four elements, L being a convergent lens, L being a divergent lens, L being a meniscus convergent lens and L being a composite lens. The element L is characterized as follows:

zs so za, zs 21 (l A diaphragm is interposed between the third group C and the fourth group D.

The arrangement and characteristics described above lead to excellent correction of various aberrations, particularly distortion, astigmatism, coma, etc.

These characteristics will now be described in greater detail.

Generally, in the retrofocus type of wide-angle lens, a member of positive refractive power, as means for the correction of distortion, is disposed in the divergent ly large'convexities or relatively small refractive indices, as specified in conditions (1) and (2) above, respectively. At the same time, the respective convex surfaces of these two elements have such curvatures that all oblique rays incident thereon are made vertical thereto, and this, together with the characteristics, as specified in conditions l and (2), serves to reduce the negative distortion created in these two elements. Therefore, such distortion that does exist can be duly corrected by the subsequent positive member L even if this member has a reduced refractive power. However, the curvature of distortion could not be reduced simply by reducing the refractive power, and therefore, it is necessary that the element L be a meniscus lens of great curvature whose concave surface has a smaller curvature than its convex surface, as seen in condition (3) above. In addition, the element L is provided with a characteristic, as specified in condition (4), so that the intervertex air space between the element L and the subsequent L, is not extremely larger than the marginal air space between these two elements. This ensures that the marginal rays will not be extremely refracted in the element L and that the marginal air space or the length of the optical path, as measured by an oblique light beam, will not be increased, thus achieving a generally less curved correction without causing substantially great overcorrection of the distortion in the marginal area.

By arranging the elements of the first group A in the manner described above, it has been found that distortion can be corrected while the curvature thereof if minimized. On the other hand, however, the relatively reduced radius of curvature R of the element L, gives birth to a disadvantage because it affects the astigmatism, especially the meridional plane, to cause overcorrection in the marginal area of the view field and under-correction in the vicinity of 80 percent of the view field. Since the meridional plane in the marginal area is closely related to the coma as described previously, the meridional plane in this area must as far as possible be kept in a more under-corrected condition than any other point in the view field. The purpose of present invention, the element L is immediately folgroup to thereby correct any negative distortion. Undev niably, however, such a member has the effect of creating an over-correction or curvature of distortion in the area near the margin of the view field. Moreover, such a phenomenon is naturally more pronounced as the angle of view is increased. Hence, the refractive power of the positive member must be minimized in order to reduce thecurvature of the distortion as much as possible when using a wide-angle lens. For this purpose, the

1 lens system of the present invention employs two meniscus divergent elements L. and L5 having relativelowed by the second Group 8 consisting of three divergent meniscus lenses of relatively great convexities, which satisfy conditions 5), (6) and (7) above. This reduces the negative refractive powers of these elements to thereby compensate for the disadvantage resulting from the radius of curvature R, of the element L i.e. the curvature of the meridional plane, and at the same time it is useful to prevent the occurrence of distortion. The forward portion of the second group is designated in this way, while the rearward portion of the same group includes the positive component L which removes the distortion occurring in the forward portion and which is a composite lens satisfying condition (8) above. The joint interface of element L is prothe lens system of the present invention. The element L8 is followed by the positive element L9 which corrects the negative distortion and positive spherical aberration caused by the preceding element L The component L, comprises joined elements formed of glass materials of different dispersive power, as given by condition so as to correct the chromatic aberrations on and off the axis.

A common feature of all of the described groups preceding the diaphragmis that each of these groups is followed by a convergent element. This is intended to correct the distortion caused by the divergent elements in each group, and is highly effective for removing the curvature of distortion.

Condition 1 l) is imposed on the fourth group D, i.e. the group disposed rearwardly of the diaphragm, to satisfactorily compensate for the breach of the sine condition which may often arise in a retrofocus type lens, as well as to correct the closely related coma in the intermediate and inner areas of the view field.

Among the various conditions enumerated above, conditions (1) and (2) are intended to minimize the possible distortion, but when the upper limits of these conditions are exceeded there will occur a great negative distortion. Such distortion, however, could be corrected readily and simply by increasing the refractive power of the element L This would, on the other hand, result in an increased curvature of distortion, which is incompatible with the primary object of the present invention of providing a lens directed to the least curved correction of distortion. When the lower limits of the conditions (1) and (2) are exceeded, no B.f. will be attained and, at the same time, the meridional plane at the portion near the margin of the view field will be subject to such an extreme under-correction that it could never be compensated for.

When the upper limits of conditions (3) and (4) are exceeded, it is apparent that the positive refractive power will be increased to cause an over-corrected distortion in the marginal area, thus failing to attain less curved correction of distortion. When the lower limits of these conditions are exceeded, there will be extreme under-correction of the distortion, which could never be compensated for by any other lens surface.

Among the conditions imposed on the second group B, those indicated by (5), (6) and (7) are based on the same concept as the conditions (1) and (2), and accordingly, they are similar in effect. When the condition (8) is not satisfied, considerable difficulties would be encountered in securing a predetermined B.f.

1f the condition (9), imposed on the third group C, should not be satisfied, difficulties will likewise be encountered in obtaining the B.f. When the condition (10) is not met, poor correction of chromatic aberration would be obtained. Also, when the condition (1 l) for the fourth group D is not satisfied, the breach of the sine condition could not be removed.

An example of the present invention and the Seidel coefficients therein are shown in the table below, where R represents the radius of curvature of each lens surface, d the intervertex distance between adjacent lenses, n the refractive index of each lens, and y d the Abbe number of each lens.

Seidel Coefficients III IV R 0.003 0.002 0.106 0.102 0.078 R, 0.0 l 3 0.006 0. 142 0. 136 0.062 R, 0.010 0.006 0.122 0.1 14 0.072 R. 0.036 0.008 0. 154 0. 1 51 0.032 R, 0.027 0.015 0.140 0.124 0.067 R. 0.000 0.000 0.012 0.016 0.654 R, 0.015 0.017 0.256 0.216 0.247 R. 0.235 0.001 -0.317 0.317 0.002 R, 0.154 0.059 0.317 0.271 0.105 R -1.266 0.219 0.537 0461 0.080 R 0.996 0.042 0.322 0.319 0.014 R '3.522 0.525 0.700 -0.543 0.081 R 0.348 0.207 0.372 0.124 0.074 R 0.359 0.214 0.383 0.128 0.076 R 0.544 0.290 0.481 0.172 0.092 R H 8.272 0.523 0.214 0.147 0.009 R 3.030 -0.870 1.042 0.543 0. 156 R 5.284 0.781 0.666 0.434 0.064 R 178.546 3.209 0.901 0.785 0.014 R, 95.728 4.919 1.172 0.667 0.034 R 1.086 0.083 0.024 0.011 0.001 R 0.001 0.004 0.061 0.020 0.091 R 0.001 0.004 0.061 0.020 0.091 R 133.161 4.474 0.920 0.619 0.021 R, 97.567 4 097 0.982 0.638 0.027 R 11.793 2.871 --2.269 0.871 0.212 R 0.101 0.133 0.431 0.078 0.103 R 41 192 -0.390 0.435 0.428 0.004 R 0.008 0.018 0.1 19 0.035 0.082 R, -1.863 0.494 0.451 0.l89 0.050 R 38.783 0.846 0.346 0.309 0.007 2 14.810 0.275 0.053 0.092 0.146

Example Focal length f I 13.2mm, Relative Aperture F/8 Angle of view 1 18 R 57.2 d, 3.9 n, -l.77279 d, =49.5 R,-43.0 d,-11.9 R,51.0 d,=3.0 n,=1.7335 d,=51.0 R, I 37.5 d, 9.3 R,-=48.2 d,- 13.5 n,- 1.732 yd,= 53.7 R,=190.0d.-0.1 R,-28.5d,=1.2 n -1.7335 7d,=51.0 R. =-17.6 d. 3.3 R,=22.5 d,== 1.0 Jr 1.7320 7d,=53.7 'R,,= 13.2 d,,,= 3.0

R,,17.6d,,-1.0 n,=1.732 yd.=53.7 R,,- 12.0 d,,=6.5 R d 1.2 n 1.51743 Filter R, w 7 d 0.5

R =350.0 d =3.0 n,== 1.83739 7d =43.5 12.08 d 12.3 n,= 1.54072 yd,,= 47.2 R s= 15.8 (1 5 0.1 R,,-17.0d =0.8 n.= 1.6968 7d.=55.6 R 7.45 d 1.7 R 11.9 d,- 2.8 n 1.59507 yd 35.6 R,,=9.0 d,,=-0.9 n,,- 1.60311 yd 60.7 R w d 1.6 R I w d I! 4.1 n 1.59507 yd a 35.6 R 10.5 d 0.6 R23 1.5 II t 'yd 23.1 R 35.4 d 0.65 R15 dz; 2.2 II8 [.44628 yd 67.2 R25 0.]. R11 (117 II I .8663 yd, 37.9 R 30.7 d, 5.7 n 1.48749 yd 70.0 R,,- 14.901 B.f. I 37.517

As has been disclosed above, the present invention provides a retrofocus type lens in which various aberrations, particularly distortion, astigmatism, spherical aberration and coma can be substantially corrected throughout an angle of view as wide as 118, and in which marginal light up to 320 percent, as measured on the first tangential plane, can be introduced for the relative aperture of F/8.

I claim:

1. A retrofocus type ultra-wide angle lens system comprising 13 air-spaced elements in four groups, said four groups including, as viewed from the object side of the system, a first group consisting of two divergent meniscus elements and a convergent meniscus element, a second group consisting of three divergent meniscus elements and a convergent cemented component, a third group consisting of a divergent meniscus element and a positive cemented component, said third group being immediately followed by a diaphragm, and a fourth group consisting of a convergent element, a divergent element, a convergent element and a cemented convergent component.

2. A retrofocus type ultra-wide angle lens system comprising 13 air-spaced elements in four groups, said four groups including, as viewed from the object side of the system, a first group consisting of two divergent meniscus elements and a convergent meniscus element, a second group consisting of three divergent meniscus elements and a convergent cemented component, a third group consisting of a divergent meniscus element and a positive cemented component, said third group being immediately followed by a diaphragm, and a fourth group consisting of a convergent element, a divergent element, a convergentmeniscus element and a cemented component, said lens system having the following characteristics:

Focal length f l3.2mm, Relative Apc rture F18, Angle of view 1 l8 R. 190.04, 0.1 R,- 28.5 d,- 1.2 11.=-1.7335 yd,= 51.0 R.- 17.6 4,- 3.3 R.-22.5 d.- 1.0 11,-1.7320 -,11,=53.7 R,,- 13.2 11,.- 3.0 R,,- 17.6 4,,- 1.0 11,-1.732 d.-53.7 R,,= 12.0 d,,- 6.5 R.- d,,=1.2 11.-1.51743 Filter Ro -P. o' 12., 350.0 111, 3.0 11, 1.83739 yd, 43.5 R,. 12.08 11.. =12.3 11. 1.54072 yd. =47.2 R15 d 0.1 R,,- 17.0 4,.-o.a 11,- l.6968 yd, =55.6 R" 7.45 4,, 1.7 R,, 11.9 11,, 2.8 11,, 1.59507 yd, =35.6 R,. 9.0 d,,- 0.9 11,, 1.6031 1 7d,, =60.7 R,,, a 11,, 1.6 R" w 11,, 4.1 11,, 1.59507 d,,

. a, R21 d2: 0.6 R23 13.] d =15 "is W237 Ru 7. 531 13 9:95 R11 41.0 11,, 2.2 11,, l.44628 'yd =67.2 e- 9 Q- ,1 =W). 1, =01? 11,, 1.8663 4., .9 R, 30.7 11,, 5.7 11,, 1.413749 7d,, =70.0

R,,-14.901 B.r.- 37.517

wherein, R subscript denotes the radius of curvature of the surface of each element; d subscript denotes the thickness of each element and the air space between adjacent elements; n subscripts denotes the refractive index of each element; and 'y d subscripts denotes the Abbe numberof each element.

* i i i i I change "element" to component line 18, change "elements" Patent No. ,728,911 Dated April 17, 1973 KNUO MORI Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 5, change "3R R 5 5" to 3R R 5R line l, change "f our" to three same line, after "L insert and same line, change "L to L same line, before "L insert one component line 16,

to element same line, after "and", insert component-- line 43, change "element" to component Column 4, line 32 change "it: to is line 59, change "designated" to designed line 63, change "element" to component Column 6, In the Example, I 1

at"'R (second occurrence), change "R 00 d 0.5"

to RQ' db 0.5

Column 8, at "R (second occurrence) change "R d =0.5" to "R o. d.' 0.5 At "R change "6.1a" to Signed and sealed this 22nd day of January 19714..

(SEAL) Attest:

EDWARD M. FLETCHER, v RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents .....nrarm-nan 

1. A retrofocus type ultra-wide angle lens system comprising 13 air-spaced elements in four groups, said four groups including, as viewed from the object side of the system, a first group consisting of two dIvergent meniscus elements and a convergent meniscus element, a second group consisting of three divergent meniscus elements and a convergent cemented component, a third group consisting of a divergent meniscus element and a positive cemented component, said third group being immediately followed by a diaphragm, and a fourth group consisting of a convergent element, a divergent element, a convergent element and a cemented convergent component.
 2. A retrofocus type ultra-wide angle lens system comprising 13 air-spaced elements in four groups, said four groups including, as viewed from the object side of the system, a first group consisting of two divergent meniscus elements and a convergent meniscus element, a second group consisting of three divergent meniscus elements and a convergent cemented component, a third group consisting of a divergent meniscus element and a positive cemented component, said third group being immediately followed by a diaphragm, and a fourth group consisting of a convergent element, a divergent element, a convergent meniscus element and a cemented component, said lens system having the following characteristics: Focal length f 13.2mm, Relative Aperture F/8, Angle of view 118* R1 57.2 d1 3.9 n1 1.77279 gamma d1 49.5 R2 43.0 d2 11.9 R3 51.0 d3 3.0 n2 1.7335 gamma d2 51.0 R4 37.5 d4 9.3 R5 48.2 d5 13.5 n3 1.732 gamma d3 53.7 R6 190.0 d6 0.1 R7 28.5 d7 1.2 n4 1.7335 gamma d4 51.0 R8 17.6 d8 3.3 R9 22.5 d9 1.0 n5 1.7320 gamma d5 53.7 R10 13.2 d10 3.0 R11 17.6 d11 1.0 n6 1.732 gamma d6 53.7 R12 12.0 d12 6.5 R0 Infinity d0 1.2 n0 1.51743 Filter R0 Infinity d0 0.5 R13 350.0 d13 3.0 n7 1.83739 gamma d7 43.5 R14 12.08 d14 12.3 n8 1.54072 gamma d8 47.2 R15 - 15.8 d15 0.1 R16 17.0 d16 0.8 n9 1.6968 gamma d9 55.6 R17 7.45 d17 1.7 R18 11.9 d18 2.8 n10 1.59507 gamma d10 35.6 R19 - 9.0 d19 0.9 n11 1.60311 gamma d11 60.7 R20 Infinity d20 1.6 R21 Infinity d21 4.1 n12 1.59507 gamma d12 35.6 R22 - 10.5 d22 0.6 R23 - 13.1 d23 1.5 n13 1.86074 gamma d13 23.1 R24 35.4 d24 0.65 R25 - 41.0 d25 2.2 n14 1.44628 gamma d14 67.2 R26 - 9.6 d26 0.1 R27 900.0 d27 0.8 n15 1.8663 gamma d15 37.9 R28 30.7 d28 5.7 n16 1.48749 gamma d16 70.0 R29 - 14.901 B.f. 37.517 wherein, R subscript denotes the radius of curvature of the surface of each element; d subscript denotes the thickness of each element and the air space between adjacent elements; n subscripts denotes the refractive index of each element; and gamma d subscripts denotes the Abbe number of each element. 